Rheostat



L Patented A131128, 1925.

UNITED STATES PATENT OFFICE.

RAY MONTAGUE CAMP, OF DAYTON'A, FLORIDA.

RHEosTA'r.

Application filed June 23, 1923. Serial No. 647,360.

T o all whom t may concern:

ABe it known that I, RAY M. CAMP, a citi-l zen of the United States, anda resident of Daytona, in the county of Volusia and State of Florida,have invented a new and Improved Rheostat, of whichthe following is afull, clear, and exact description.

This invention relates to a rheostat, and has for an object theprovision of a rheostat in which very line adjustments are easilyeffected.

Another object concerns the provision of a rheostat which is animprovement over the form of rheostat shown in my copending application,Serial No. 640267, filed May 19, 1923, entitled Rheostat A furtherobject concerns the provision of means whereby a minimum number ofsimply constructed parts are used so that the strength and durabilityare increased and the liability to get out of repair is reduced to aminimum.

The invention is illustrated in the drawin s, of which l 4igure 1 is aside elevation of the device;

Fig. 2 is a section taken on the line 2 2 of Fig. 1;

Fig. 3 is a section taken on the line 3-3 of Fig. 2; and

Fig. 4 is a perspective of the contact shoe.

The form of the invention shown in the drawings is a preferred form,although it is understood that modiiications in the construction 'andarrangement of the parts and in thel character of the materials used maybe adopted without departing from the spirit of the invention.

The invention in general includes preferably a cylindrical or rotatablesupport of insulating material, preferably provided with a spiral groovein its surface, 'said groove having preferably a rectangular crosssection in which is laid a resistance wire, preferably of ribbon formand continuous. Over this support and ribbon is placed a conducting nut,preferably threaded andy held thereon, which as the support is rotatedwill move therealong in contact with the ribbon in either direction,depending upon the direc-tion of rotation of the support.l f

This nut isprovided with a connection which makes contact with theoutside circuit, and also affords means for guiding the nut to hold itfrom rotation. The support is held in a frame from which it may beeasily di'smounted. Connected with the nut but easily removabletherefrom is a contact shoe formed of resilient material adapted toextend into the groove or thread on either or both' sides of the nut tomake a more perfect contact with the ribbon.

The invention as illustrated in the drawings includes a frame having afront plate 1 and a rear spring plate 2 connected by a cylindricalportion 3 containing a body of insulating material 4a. This cylindricalportion is cut away throughout most of its length on the upper sidethereof, and the insulating body portion 4 is provided with a groove 4along the bottom of which a contact strip or track 5 is disposed. Thistrack at one end, nearthe front wall, is provided with a connection 6leading to a binding post 7 mounted on the plate 1 but separatedtherefrom electrically by insulation 8.

Mounted also on the front wall or plate 1 is a second binding post 9which, however, is in electrical contact with the plate 1 and throughthe cylindricalfportion 3 and the rear spring plate 2 connects with theother parts in circuit, as hereinafter to be described. The rear plate 2is provided with a depressed portion 12 in which fits 'a tapered orinclined nut or screw 13 which 1s embedded in the end of an insulatingbody portion 14, preferably cylindrical. This body portion is providedon its surface with a spiral thread or groove of rectangular crosssection in which is held a preferably continuous resistance ribbon 15,one end of which is embedded in the body portion and the other end ofwhich is connected to the screw 13.

The other end of the support or cylindrical body portion 14 is providedwith al stem 16 passlng through the front plate 1, and on its other endcarries a knob 17. Surrounding the cylindrical body portion is ametallic conducting nut 18, preferably split at 19 and held together bya spring 20: This nut is adapted to surround the ribbon and the supportand travel along the ribbon in one direction or another as the stem 16is rotated in one direction or another. Dependent from the lower portionof the nut is a contact finger 21. The contact linger 21 bears on thetrack 5 acting as a means for conducting the current to said track andalso to prevent rotation of the nut 18 which naturally tends to rotatewhenever the body portion 14 is rotated.

Therefore, the slightest rotation of the knob 17 will vary the amount ofwire which is in contact between the end 18 andthe screw 13.. A plug 22is mounted in a suitable groove or aperture between the split end of thenut 18, and to this plug is connected a strip of flexible material 23,preferably resilient or spring metal in the form of a shoe extendiglaterally from said plug and depending downwardly to lie in a groove orthread in thesupport 14 and contacting with the ribbon therein. Theupper surface of the plug is provided with a groove 24 in which thespring 20 lies, this spring tending, therefore, to hold the plug inplace. B removing the spring from bearing on t e`plug, the plug can beremoved and with it the contact shoe 23. The

. nut on its lower .portion is provided with a stop arm 25 so that asthe nut travels Y towards the rear of the support 14 the stop arm 25will engage the rear plate 2 to prevent or make more diflicult furtherrearward movement .of the nut.

By using the ribbon the warping, caused by expansion, is up and down, sothat distortion of one coil cannot affect the other. The coil spring onthe nut now performs three distinct functions: lirst, holding theexpanding nut on the insulated body portion 14; second, making contacton the plug 24; also forcing the plug and contact shoe down, making surecontact with the ribbon. The shoe is adapted to travel just ahead of thenut so that in case of expansion of the ribbon a final adjustment can beo btained, since, should the ribbon come in contact with the nut' itwill have no efect. It is also to be noted that as the nut travels tothe end of the support 14 the stop arm 25 will engage the spring plate 2and if pushed too far will break the circuit between the plate 2 and thescrew 13 and thereby act as(A a switch.

The electrical circuit through the apparatus is as follows: From thebinding post 9 to the front plate 1, cylinder 3, rear platel 2, screw13, wire 15 to the shoe 23, plug 22, spring 20, nut 18, contact finger21, track 5, connection 6, and binding post 7. The ends. of the spring20l maybe hooked over ears such as 2Oa formed on the sides of the nut18. That portion of the wire 15 which lies between the nut and the screw13 is the portion of the resistance which is in circuit.

It will be apparent from the description of the operation that verysmall quantities of wire can be drawn into or out of the circuit by asimple manipulation of the invention. Because of the fact that the pitchof the thread or groove in the body portion 14 is generally very finethis sensitiveness and line adjustment can be easily achieved. A firmand sure contact with the ribbon is at all times insured regardless ofany expansion of the ribbon which vlmay take place. Furthermore, toogreatmovement of the nut toward the rear will automatically causeA thebreaking of the circuit. The contact shoe is easily removable for repairand adjustment, the entire apparatus, including the relatively smallnumber of simple parts making the simplicity of the entire device amatter of fact.

What I claim is l. A rheostat including an insulating sup- Y port havinga spiral groove in itssurface, a threaded conducting nut embracing4 saidsupport, a conductor in said groove, a spring plate supporting andconnected to the rear end of the support, and a stop on the nut toengage said plate when the nut has'traveled a delinite distance to therear of the support whereby further movement of the nut will move thespring plate away fromt-he support to break the connection therebetween.

2. A rheostat which includes an insulating support portion having aspira-l groove in its surface, a threaded conducting' nut embracto holdit in the aperture, a contact shoe connected to said plug and dependenttherefrom into the groove adjacent the traveler nut, and a conductor insaid groove withvwhiclisaid shoe makes contact.

RAY MONTAGUE CAMP.

